Deformation and Stress Analysis of the Deepwater Steel Lazy Wave Riser Subjected to Internal Solitary Waves

The dynamic response of the steel lazy wave riser (SLWR) subjected to the internal solitary wave is a key to assessing its application feasibility. The innovation of this paper is to study the dynamic response properties of the SLWR with large deformation characteristics under internal wave excitation. A numerical scheme of the SLWR is constructed using the slender-rod theory, and the internal solitary wave (ISW) with a two-layer seawater model is simulated by the extended Korteweg-deVries equation. The finite element method combined with the Newmark-β method is applied to discretize the equations and update the time integration. The ISW excitation combined with vessel motion on the dynamic deformation and stress of the SLWR is investigated, and extensive simulations of the ISW parameters, including the interface depth ratio and density difference, are carried out. Case calculation reveals that the displacement of the riser in the lower interface layer increases significantly under the ISW excitation, and the stresses at a part of both ends grow evidently. Moreover, the mean value of riser responses under a combination of vessel motion and ISW coincides with the ISW-induced ones. Furthermore, the dynamic responses along the whole riser, including the displacement amplitudes, bending moment amplitudes, and stress amplitudes, almost increase with the increase in interface depth ratios and density differences.